United States has a social institution called "tipping." Basically, the price on the menu at any place which serves food is not the real price. The real price is 15% higher. However, Miami Beach is the exception, where some restaurants and bars include the tip, so make sure to check your bill to avoid double tipping.
The standard tip is 15%. If you are dissatisfied with the service you may leave less, or even nothing at all, but if you were well served 20% is appreciated. Taxis work the same way. It is considered very rude not to pay the gratuity.
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